In magnetic resonance (MR)-based imaging methods, there may be deviations in the magnetic fields, more particularly in the spatial distribution of their magnetic field strengths, from their theoretically prescribed and calculated values, as a result of which image-geometrical distortions occur. This is particularly disadvantageous within the scope of applying a method based on a quantitatively accurate geometric illustration of the regions to be examined in an examination object because this can significantly reduce the informative value of the generated images.
It is well known that phantoms provide an option for detecting geometric distortions that occur in a particular MR sequence. A phantom is a hollow base body that delimits an interior volume, into which a medium is filled; this is often water since this has permeability to radiation that is comparable to human tissue. However, there are strong variations in the signal intensity when carrying out MR imaging methods, particularly as a result of increases in dielectric effects when using high basic field strengths of the applied magnetic field above 3 tesla, which is why satisfactory results cannot be obtained with relatively large phantom volumes in the case of magnetic field strengths above 3 tesla. This is redressed by using oil instead of water as fluid filled into the phantom.
In the integrated application of MR- and PET-based imaging methods, there is a need to generate both PET imaging data with activity and MR imaging data using a phantom. By way of example, this may be required for testing the PET attenuation correction. In the process, the introduction and mixing of the activity of phantoms filled with oil is difficult because the activity is present dissolved in water; this leads to significantly increased temporal exposures of the operator.
In this context, it has been suggested to transfer the active liquid into an oil-water emulsion. However, this method leads to a significant radioactive exposure of the operator as a result of an increased temporal exposure. Furthermore, the options of MR imaging are limited by the so-called chemical shift of the oil.
DE 10 2005 045 679 B3 has disclosed a magnetic resonance imaging (MRI) arrangement with an MRI phantom and a method for determining the homogeneity of the magnetic field. Herein, an MRI phantom with a hollow base body that delimits an interior volume is separated by way of a separation element, as a result of which a main chamber and a partial chamber are created. Here, the main chamber is delineated from the partial chamber such that a gaseous bubble can enter the partial chamber as a result of a change in the spatial orientation of the MRI phantom in the gravitational field.
US 2008/02655882 A1 has disclosed an MRI- or an MRS-phantom, in which a plurality of subdivisions are provided in a phantom housing, which can each be filled separately with a fluid.
U.S. Pat. No. 4,818,943 has disclosed a phantom for imaging systems, wherein the phantom has a cylindrical housing with a central axis and a defined interior volume. Here, the interior volume is separated by means of separation elements, and so two chambers are created, which can be filled by different fluids.